Apparatus for the estimation of the distribution of the cargo in a ship



Dec. 23, 1958 K SWENSON 2,865,566

APPARATUS FbR THE ESTIMATION OF THE DISTRIBUTION OF THE CARGO IN A SHIPFiled May 10, 1954 2 Sheets-Sheet 1 X A L 8 I 1 L7 L2 L5l4- L W a a "J mJ & PAM

ATTORNEYS Dec. 23, 1958 K. SWENSON APPARATUS FOR THE ESTIMATION OF THE 62 mm t e 5 m 6 8, m 2 e DISTRIBUTION OF THE CARGO IN A SHIP Filed May10, 1954 INVENTOR fi urf Lennarf swemso/z United States Patent APPARATUS.FOR THE ESTIMATION OF, THE DIS- "TRIBUTION OF THE CARGO IN A SHIP KurtLennart Swenson, Gothenburg,

Aktiebolaget Gotaverken, ,poration of Sweden ApplicationMay-10,19,54,Seri al'No. 428,784 C ms Pri r y, pp atio S e M y.. .6,.19 2Claims. '(Cl."235-161) Sweden, assignor to 'Gothenburg, Wedcn, a cor- Ina ship for transport purposes there are different spaces foraccommodation of the cargo which spaces are dimensioned in such mannerthat they will be completely-filled if the specific weight of the loadis comparatively low. For this reason when loading the ship with amaterial; of a comparatively high specific weight, a-considerable partof "the load space is left empty, and in suchcase the distribution-ofthe cargo in said spaces may be chosen in different ways. The so-calledtrim indicates the distribution of the cargo in the longitudinaldirection of the ship and corresponds to the difference between thedrafts at the ends of the ship. Many important factors are dependentonthe trim, for instance, the propellerefficiency, the speed of theship, the behavior or performance in-the sea and the general comfort onboard. The distribution of the cargo should therefore'bechosen so as toproduce a trim which is most advantageous in said respects.

-Moreover, the distribution ofthe cargo in the longitudinal direction ofthe ship determinesv the tensions or stresses in the longitudinaldirection of the ship. The deformation of the ship owingto thesetensions is not visible to such anextent as the trim 'but in certaintypes of ships, particularly in tankers, it is possible to, choose thedistribution-of the load in so many ways that with an extremelyunsuitable distribution of the cargo and under otherwise'unfavorablecircumstances theship may be subjected to inadmissiblygreat tensionswhich may result in the formation of cracks in the material,perhaps-with the risk oftotal'rupture.

The theory of calculating the trim of a ship is generally known to theships officers. The problem in this connection isto obtain the necessarydata, for instance, the position of the center of gravity of thedifferent load spaces and hydrostatical data. The procedure incalculating the resulting bending moment and the resulting stresses inthe longitudinal ,directionof, the ship is, however, more complicatedand is mostly unknown to the ships officers. It is therefore desirableto.have a possibility of controlling or checking the distribution of theload with respect to the resulting trim and the stresses caused thereby.Since said stresses reach their maximum value when the ship occupies acertain position in the waves of the sea, the problem is morecomplicated owingto the hydrostatical conditions being difficult todefine satisfactorily.

A certain conception of the magnitude of the resulting stresses may,however, be obtained by the so-called standardized strength calculation.In this calculationit is assumed that the ship is carried by waves thedistance between the wave-crests of which being equal ,to the length ofthe ship and the depth of which i. e. the verticalv distance betweenwave-crest and wave-hollow, ,being equalto one twentiethcf the length ofthe ship. The p t q c th h p ic is thenv ubme s in te a d whichthusactually carries theship including the cargo thereof, canbe indicatedgraphically'ina diagram. The displacement curve contained in thisdiagram, the appearlevers fore and after said plane.

ance of which varies in dependence on the trimming position of the shipanddependingon whetherthe ship is disposed with the center thereofovera-wave-crestand with the stern and the stern over two adjacentwavehollows, the hogging-pos ition, or whether the: stem and the sternare located each on a wave-crest, with a wavehollow beneath the shipatthe center'thereof,""fthe-saggingposition, confines an area, which-isas "large-as but quite different in shape from the area confinedby acurve indicating the weight ofthe ship includingthe cargo thereof asdistributed in the longitudinal direction of the ship. Acombination'ofthese two curvesgives a loading curve, and if 'thelatter isintegrated--twice,=a curve of shearing forces isfirstobtained and thencea curve relative to the bending-moment which latter gives the stressessought in connectionwith' the section modulus calculated for the ship.The performance ofa calculation of this type requires avery longtime-evenffor1a single case of loading.

The object of the present invention isto providean apparatus by means ofwhich the suitability of a certain load distribution both with therespect to the trim and the stresses in the bulk owing to thelength-wise bending moments may be ascertained. {The invention ischaracterized in that the apparatus is constituted by anelectricbalancing device including ,a group of series-coupled resistances whichare adjustable to valuesproportional to the products of the weights ofthe loads on one side of an imaginary plane dividing the ship intoone'forebody and one after-body, and the distances of saidiloads fromsaid plane, asecond group of series-connected resistances which areadjustable in a similar manner with respect to the loads on the-oppositeside of saidplane, a first additional resistance which is M proportionalto the moment of the bulk weight and the displacement with respect tosaid plane and a second additionalresistance which is proportional tothe hydrostatic effect of the forebody and the after-body and of themoment of'the bulk weight, a switching means being provided foralternately inserting the resistances in one of two electric balancesin'such manner that the one branch of the one balance is constituted byone of said groups of resistances and the other branch is constituted bythe other group/of resistances in series with said first additionalresistance, while the one branch of the second balance is constituted bythe series connection of said both resistance groups, the' branches ofsaid balances each being interconnected through the resistance part of apotentiometer, the movable tap of which in a ,balancedcondition ofsaid'baltively, said forces being balanced by a system of upwardlydirected displacement lifting forces. The effect of the last-mentionedforces may besubstituted -by-a single upwardly directed force equal tothe magnitude of the displacement and located in its centre of gravityAA, Fig. 1. The trimming moment is then equal to the algebraic sum ofthe moments of the loads and of the bulk weight with respect to theplane AA, signs being used for If instead of the plane AA anotherarbitrary plane X-.-X is chosen the same trimming moment may becalculated by adding;to..the algebraic sum of the moments of theloads.andthe bulk weight with respect to,the newplaneX-TX,themQment of thedisplacement lifting force with respect to jthesame plane while usingthe same rule for thesigns as men-- tioned above, the force beingintroduced with a negative sign. The formula for the trimming moment Tmay generally be written as follows:

1 in which I=2'vLx+f '01) Y v=the weight of each partial load,

Lx=the length of the lever to the planeX-X for each partial load,

-h=a hydrostatic characteristic an d in which f'(h) includes, on the onehand, the moment fof the bulk weight and, on the other hand, the momentofthe displacement with respect to the plane XX and is a constant valueat a given displacement condition. For .the levers the above-mentionedsign-rule shall be applied. The trirnof the ship to be measured is notdirectly propo rtional to the trimming moment but is also dependent. on.the hydrostatic conditions, particularly the draft. These hydrostaticconditions are represented by the factor f"(h) and its value is equal tothereciprocal value of the trimming moment required at a certain draftto trim the ship one trimming unit, for example 1 inch. The function off"(h) is contained in the scale of potentiometer unit 21-22 laterdescribed and a different scale for that potentiometer is required foreach value of mean draft used with the apparatus. The trim t maytherefor be written as follows:

-When calculating the trimming moment of the ship according to theaforesaid, the ship and its load may at first be assumed to be balancedon a support in the cen Qtr'e of gravity of the displacement. Forcalculating the lengthwise bending moment in a section YY, Fig. 2,dividing the ship into a fore-body and an after-body, a correspondingsimplification as to the hydrostatic forces may be made.' In such caseone must consider each part of the ship separately and concentrate thetwo parts of the displacement to the respective centres of gravitythereof. Thus, the ship may be considered to be lying on two supports inthe planes BB and CC. That this is in agreement with real facts, willappear from the following: If a weight is placed at the centre of theship, the ship will be subjected to increased sagging stresses (negativemoment). If, however, the weight is placed at one of the ends of theship the hogging stresses will be increased (positive moment).Therefore, a plane must ex- ,ist in an intermediate position between thecentre and the respective ends of the ship in which plan'e an increaseof the weight does not result in any positive or negative increase ofthe moment. In each part of the ship the resulting moment is thealgebraic sum of the moments of the load and the bulk with respect tothe plane BB and .CC respectively, and the total lengthwise bendingmoment in the plane Y-Y is the sum of the two resulting moments from thefore-body and the after-body of the ship.

As mentioned in connection with the calculation of the trimming moments,the resulting moment in each part of the ship may, however, becalculated with respect to an arbitrary plane, while paying due regardto the effect of the moments of the hydrostatic forces with respect tothis new plane. It is therefore suitable to calculate the moments withrespect to the common plane YY for the two parts of the ship. The totallengthwise bending moment M in the plane YY may therefore be written inwhich v=the weight of the partial loads Ly=the length of the lever tothe plane YY for each partial load h=a hydrostatic characteristic 7';f"(h) includes the hydrostatic effect of both the fore body and theafter-body and, moreover, the moments from the parts of the bulk, sincethese are constant values. designates in case the numerical sum.

When measuring by means of a single apparatus the trim and thelengthwise bending moment, it is suitable that the plane X-X beidentical with the plane YY, which is chosen so as to lie where thelengthwise bending moment has its maximum .value or elsewhere where itis desired to know its magnitude.

The Formulas 1 and 2 may then be written as follows:

in which 2 is the algebraic sum and 2" is the numerical sum of themoments of the'ditferent loads.

The invention. will hereinafter benmore fully described with referenceto Figs. 3 and 4 of the drawing. Fig. 3 shows a circuit diagram of theapparatus and Fig. 4 shows one embodiment of an apparatus according tothe invention;

The electric balancing means according to Fig. 3 includes a currentsource 9, a switch 10, two known, constant resistances R and a group ofseries-connected resistances 11, 12, 13, and 14, which are adjusted tovalues proportional to the products of the weights v -v of the loads onone side of the plane XX (Fig. 1) and their distances L -L from theplane XX. The corresponding load spaces are designated 1-4 in Fig. 1.The balancing means comprises further a second group of series connectedresistances 15, 16, 17 and 18 which are adjustable in a similar mannerwith respect to the loads in the after-body of the ship, thecorresponding load spaces being numbered as 5-8. A resistance 19 isadjustable to a value proportional to f'(h) and a resistance20-corresponds to f(h). The resistance portion of a potentiometer isdesignated 21, the movable tap of the potentiometer being designated 22.A second potentiometer has a resistance portion 23 and a movable tap 24.The potentiometers may alternately via a galvanometer 25 be connected toa point between the two resistances R The potentiometer 21, 22 isprovided with a plurality of scales 26, 27 for different draftscorresponding to the factor f"(h). Switches by means of which twodifferent electric balances may be obtained are designated 0 O and 0 Ifthe switches are in the positions indicated with full lines in Fig. 3,the two resistance groups 11-14 and 15-18 are connected in series to theone side of the potentiometer 23, 24, the other side of which beingconnected to the resistance 19. The potentiometer 21, 22 and theresistance 20 are then switched out of circuit. The operating partsconstitute in this case the one electric balance, the one branch ofwhich being constituted by 2"vLy and the other branch of which beingconstituted by f"'(l1). In this setting of the apparatus the lengthwisebending moment M of the ship may be determined. The balance consists inthe embodiment shown of a Wheatstone bridge which in a manner known perse is operated in such manner that the two branches are balanced bymeans .of the potentiometer 23, 24, and the current through thegalvanometer is zero. The potentiometer scale may advantageously be suchthat in this case the lengthwise bending moment M or, if desired, thecorresponding bending stress is indicated. The scale may be providedwith marks indicating the limits of the permissible range of variationsof the moment or stress.

It the switches 0 O and 0 are set in the positions indicated by brokenlines in Fig. 3, a bridge is obtained the one branch of which beingconstituted by the resistance group 11-14 and the second branch beingconstituted by the resistance group 15-18 in series with the resistance19. In this case the values E'vLy and j'(h) are balanced over oneanother via the potentiometer 21, 22, the state of balance being reachedwhen by ad'- justment of the potentiometer arm 22 the galvanometer 25reads zero. The trim t is then obtained in an analogous manner and canbe read on the scale 26 or 2'1 for thedf'a'ft'iri question;"As'the'r'h'ovabl armor 22 will usually have to be adjusted in onedirection or another. the zero point on the trim scale can be located ata middle point on the scale. Depending upon load distribution, the trimwill be either positive or negative (by stem or by stem, respectively)from zero and will be properly indicated dependent upon the direction ofmovement of the arm 22 required to obtain bridge balance. Should thetrim and/or the lengthwise bending moment not lie within the permissiblelimits a different load distribution must be tried by changing theresistance values of one or both of the resistance groups 11-14 and15-18 until a load distribution is reached which is acceptable both withrespect to the trim and to the lengthwise bending moment.

The apparatus according to the invention may for example be built in themanner indicated in Fig. 4, according to which the casing of theapparatus consists of two boxes 30 and 31 the latter being pivotallyconnected to the box 30 at the lower end thereof so that it can be movedfrom a vertical to a horizontal position and vice versa. The circuitelements in the boxes are interconnected by means of conductors 32 and33. The panel of the box 30 is subdivided into different sections orfields. The section 34 indicates the name of the ship and a schematicillustration of the positions of the different load spaces in the ship.It is assumed that the ship comprises 25 load and storage spaces eachbeing represented by a potentiometer r corresponding to the resistancesof the two groups of resistances shown in Fig. 3. These resistances aregrouped together in a surveyable manner in difierent fields 35, 36, 37,38 and 39.

The box 30 accommodates the resistance 20, the movable part 22 of thefirst potentiometer cooperating with a plurality of scales, the part 24of the second potentiometer and the resistance 19. The galvanometer isdesignated 25 and a handle for actuating the switches shown in Fig. 3simultaneously is designated 48. It has three different positions,namely two end positions for switching in the two different balances andan intermediate position in which the apparatus is switched off. Lamps41 and 42 indicate which of the two balances is connected into circuit.A space 43 contains directions for the use of the apparatus, tablesshowing the hydraulic characteristics of the ship at different degreesof loading, the capacity of the load and storage spaces and suitablecorrections for obtaining a better load distribution if the distributionfirst chosen should prove to be unsuitable.

The apparatus is set or adjusted by means of the values obtained upon astandardized calculation of strength. When using the apparatus a certaindistribution of the load may be chosen, which according to priorexperience is likely to be suitable. In this connection the liberty ofchoosing the distribution may be limited in certain respects. So, forinstance, the load may consist of oils of different types and quantitiesin which case it may be necessary to accommodate a certain type of oilin a certain space due to its quantity, while another type of oil cannotbe accommodated in a given load space due to the composition of thistype of oil.

When this preliminary load distribution has been chosen the resistances11-18 are adjusted to the corresponding values and the resistances 19and 20 are then adjusted according to the existing hydrostaticconditions at the total load in question.

For judging the trim the handle 40 is thereafter turned to the one endposition corresponding to the trim and the member 22 is then turneduntil the pointer of the galvanometer 25 occupies the zero position. Thevalue of the trim may thereafter be read on the scale of the member 22.When the handle 40 has been turned to its other end position the member24 is turned until the galvanometer again shows the zero value,whereafter the sought moment or the corresponding bending stress may beread on the scale of the member 24. If the chosen load distributionshould prove to be unsuitable, the procedure has to be repeated after asuitable redistribution of the load as determined by the resistancesrepresenting the partial loads, which may be effected with the guidanceof a table specially composed for this purpose, so that both the trimand the stresses at least show acceptable values.

What is claimed is:

1. An apparatus for estimating the influence upon a ship of thedistribution of a certain quantity of cargo therein, comprising a firstgroup of series-connected resistances, means to adjust said resistancesto represent the moments with respect to an imaginary plane dividing theship into a fore-body and an after-body and caused by parts of saidcargo when placed in various holds in the fore-body of the ship, asecond group of series-connected resistances, means to adjust saidresistances of said second group to represent the moments with respectto said plane and caused by parts of said cargo when placed in variousholds in the after-body of the ship, a first additional resistancerepresenting the trimming mo ment of the Weight of the hull and thehydrostatic displacement lifting force with respect to said plane, asecond additional resistance representing the lengthwise bending momentof the Weight of the hull and the hydrostatic displacement liftingforce, a dual purpose electric balancing device containing a supply ofelectric current, two reference resistances and a galvanometer, a firstpotentiometer, a second potentiometer, a switching device foralternatively arranging the various resistances in relation to thebalancing device in such a manner, that for one purpose a first branchis constituted by one of said groups of resistances and a second branchis constituted by the second group of resistances in series with saidfirst additional resistance, said first and second branches beingconnected by said first potentiometer, whereas for the other purpose athird branch is constituted by the series connection of both groups ofresistances and a fourth branch is constituted by said second additionalresistance, said third and fourth branches being interconnected by saidsecond potentiometer.

2. An apparatus as claimed in claim 1 arranged for the estimation of theinfluence of various quantities of cargo, wherein said firstpotentiometer is provided with different scales for different values ofthe draft of the ship.

References Cited in the file of this patent UNITED STATES PATENTS1,826,762 Franklin Oct. 13, 1931 2,123,142 McMaster July 5, 19382,443,098 Dean June 8, 1948 2,520,428 Nilakantan Aug. 29, 1950 OTHERREFERENCES Laws Electrical Measurements, McGraw-Hill Book Co., Inc.,1917, Fig. 96 on page 171.

